A large number of industrial processes involve the use of volatile organic compounds (frequently referred to as VOC's) whose emission into the atmosphere is objectionable because of environmental pollution or the expense of replacement in the process scheme, or both. In either instance it is becoming increasingly necessary to reduce such emissions in a highly effective manner to meet stringent government requirements or to improve the economics of the process.
Accordingly many methods for emission reductions have been proposed which may involve condensation and recovery of the VOC's in the liquid phase, combustion to environmentally acceptable substances such as CO.sub.2 and H.sub.2 O, preferential adsorption on a porous or microporous material such as activated carbon or zeolitic molecular sieves, or absorption in a hydrophilic fluid such as an oil-in-water emulsion as in the HEC process. Combinations of these techniques are frequently employed.
The chemical and physical properties of the light aliphatic alcohols, i.e., methanol, ethanol, n-propanol and isopropanol, coupled with their generally pleasant odor, make this group of solvents highly preferred in a wide variety of industries. As a solvent, ethanol's use is exceeded only by water, and is a key raw material in the manufacture of drugs, plastics, lacquers, polishes, plasticizers, perfumes and cosmetics. The other light alcohols find similar uses. It is found, however, that the adsorbents typically employed in solvent recovery, i.e., activated carbon, low-silica zeolites, aluminas and silica gels, are not very effective for the adsorption and retention of the light alcohols. This is especially true when the fluid stream being treated contains a relatively high concentration of water which is preferentially adsorbed with respect to the alcohols. To increase the selective adsorption of alcohols under these circumstances it has heretofore been proposed to employ highly siliceous molecular sieves, such as silicalite, which are less hydrophilic than low-silica zeolites and consequently exhibit a greater affinity for the less polar alcohols. These organophilic molecular sieves are ordinarily employed in the form of bonded agglomerates prepared by admixing the molecular sieve, after calcination to remove the organic templating agent present as organic cations or simply occluded in the pores system, with water and an inorganic oxide matrix material such as a clay to form an extrudable mass, and firing the extrudate particles to set the binder and activate the molecular sieve.